Simplify $\left(-4x^2+7x-9\right)+\left(6x^2+7x+8\right)$(−4x2+7x−9)+(6x2+7x+8).
Simplify $\left(-8x^2-3\right)+\left(-4x^2-8x\right)$(−8x2−3)+(−4x2−8x).
Simplify $\left(3x^3-9x^2-8x-7\right)+\left(-7x^3-9x\right)$(3x3−9x2−8x−7)+(−7x3−9x).
Simplify $\left(\frac{1}{2}x^2-\frac{1}{4}x+\frac{1}{2}\right)+\left(\frac{1}{3}x^2+\frac{2}{5}x-\frac{1}{4}\right)$(12x2−14x+12)+(13x2+25x−14).